Method for manufacturing gypsum from anhydrite



. Patented Dec. 15, 1925.

UNITED STATES 'PATENT OFFICE.

' MARIE QIJLEQN S tilt/1TH, OF NEW BRUNSWICK, NEW JERSEY.

METHOD FOR MANUFACTURING GYPSUM FROM AN'HYDRITE.

No Drawing.

To all whom it may concern:

Be it known that I, MARIE FAuNswn'ri-I,-

' citizen of the United States, residing at New Brunswick, in the countyof Middlesex and State of New Jersey, have invented certain new anduseful Improvements in Methods for Manufacturing Gypsum fromAi'ihydrite,

of which the following is a specification.

This invention is a method for vnranufacturin gypsum from anhydrite.

Anhydrite anhydrous calcium sulfate) as such, is of very slight use;' itis plentiful enough, occurring in gypsum mines and as a icy-product incertain industries. But there is practically'no commercial use for it.If,

however, the anhydrite can be hydrated to 1, 1918 says that in a sampleof anhydrite that stood in contact with water' for six years, aboutone-third of it was hydrated. J. L. McCaleb, Amer. Chem. Jour. 11, 34,(1889) took anhydrite in the form of 4 a fine powder and observed therate of hydration over a period of thirty-six weeks. From hisexperiments, he concludes the hydration would be complete in about twoyears.

Applicant finds that as the anhydrite is ground finer and finer, therate of hydra-.

tionis slowly increased. Applicant has discovered, however, that a mostunusual and unexpected increase in the rate of hydration takes placewhen the grinding was carried to a stage where the particles varied insize from 135 microns down to the colloidal with an average size ofabout 18 microns. The curve showing the rate of hydration took asuddenand sharp. upward'bend when the grinding was carriedto this stage showving a sudden and sharp mcrease 1n the rate of hydration. As the grindinwas carried finer and finer, the rate 'oiiv ydrationim creased out ofall proportion to the fineness of the grinding.

'osum board and the like; ortland cement, a prod- Application filedMarch 11, 1925. Serial No.14,835.

More specifically, applicant has found that where the particles vary insize from 3 mm. down to about of a millimeter, the hydration that takesplace in three weeks slowly increases from a fraction of one per cent upto about five or six per cent, a rate that commercially and industriallyis useless, and that would require from fifty weeks to some years forthe completion of the hydration. When, however, the grinding was carriedto-a stage where the particles varied from 30 microns in size, down tothe colloidal, with an average particle size of 7 microns, the samplewas completely hydrated in three weeirs.

With an average particle size of: 8 microns,

the sample was 33% hydrated in. three Weeks. Vith an average particlesizeof 9 microns, the sai'nple was 33% hydrated in three weeks. ilheseand other results are tabulated be complete hydration, as related to thesize or The rate of hydration and the time for the particles, isindicated in this tabula-- .tion i iiiiiiia A Time! ll in i 1 m r or ae1 Approximate minimum particle com lete to mum size size in by agypsumsize in microns tlon in three microns weeks Weeks l8 18 14 12 13 23 l0ll '27 9 9 33 8 4 7 3 I The grinding may be carried out in any desiredtype of mill, such for example, as a ball, pebble or colloid mill. Thegrinding may be,- and preferably is, a wet grinding, but may be dry orwet or partly dry and p'artl wet. The invention is not to be limite togrinding in any particular type of mill, or to a grinding which is wetor dry or both. These details may be" varied within the scope of theinvention.--

. After the material is quired fineness, t is by with an excess ofwater, and preferably agitated'from, time to time, or continuously.

Agitation increases the rate of hydration.- 'Steam may be used-ifdesired. The details ground to the re rated by mixing 1. {a method forakmhydnm which comp ms grinding ana betwew 118 limits in which notexceed subsfian- 2m szvel' z'gge size 0f Wine the im'gest 1 0 not exceedsubstaniafiy 30 miuf substantially he gram! anning gypsum from grmdmgunemass m sub i'anhai gypsum from grmdmg nnliv- MARI E FA. R SWORT H:-

